`a) x/6 = y/-7 ; x/3 = z/-8`
`x/6 = y/-7 = z/-16`
`x/6 = (2y)/-14 = (3z)/-48`
`⇒` `{x-2y+3z}/{6+14-48} = {56}/{-28} = -2`
`=>` `{(x=-12),(y=14),(z=32):}`
Vậy `(x;y;z)=(-12;14;32)`
`b)3x = -4y = 2z`
`⇔ x/4 = y/-3 = z/6`
`⇒` `x/4 = (2y)/-6 = (3z)/18`
`⇒` `{x-2y+3x}/{4 + 6 + 18} = {56}/{28} = 2`
`=>` $\begin{cases} x=8\\y=-6\\z=12 \end{cases}$
Vậy `(x;y;z)=(8;-6;12)`
`c)` `2x = -3y ; 7y = -10z`
`⇔ x/-3 = y/2; y/-10 = z/7`
`⇔ x/15 = y/-10 = z/7`
`⇒` `x/15 = (2y)/-20 = (3z)/21`
`⇒ {x-2y+3z}/{15+20+21} = 56/56 = 1`
`⇒` $\begin{cases} x=15\\y=-10\\z=7 \end{cases}$
Vậy `(x;y;z)=(15;-10;7)`
`@thew`
